Engine manufacturers are reducing engine displacement and boosting air supplied to engines to provide a desired level of engine power with reduced fuel consumption. For example, a turbocharged four cylinder engine can output power that is substantially equivalent to a normally aspirated six cylinder engine. And, reducing an engine from six cylinders to four cylinders can reduce engine friction and pumping work, thereby reducing engine fuel consumption. In U.S. Patent Application Publication 2003/0000211, an engine system that routes exhaust gases to a turbocharger via two separate exhaust manifolds is described. The system purportedly improves delivery of exhaust gases to the turbocharger.
The inventors herein have recognized various shortcomings with the exhaust manifold disclosed in U.S. Patent Application Publication 2003/0000211. For example, the system requires two separate exhaust manifolds. Further, the engine air-fuel control may be complicated by the two exhaust manifolds. Further still, the described turbocharger appears to require two exhaust gas inputs.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: combusting an air-fuel mixture in each cylinder of an engine; routing exhaust gases of each cylinder through a single exhaust manifold; deactivating solely one exhaust valve of each cylinder of the engine during a first engine operating condition, the deactivated solely one exhaust valve of each cylinder deactivated for at least two engine cycles; and activating the solely one exhaust valve of each cylinder during a second engine operating condition.
By deactivating a single exhaust valve of each cylinder of an engine exhaust gases produced by combustion in the cylinders can be routed to a turbocharger in a way that increases turbocharger efficiency at lower engine speeds. In particular, when a first exhaust valve of a cylinder is deactivated at lower engine speeds, the velocity of exhaust gases expelled from the cylinder via a second exhaust valve can be increased to impart additional energy to a turbocharger located in the exhaust system downstream of the cylinder. Further, exhaust gas residuals can also be reduced when one of the two exhaust valves is deactivated at lower engine speeds. The increased turbocharger efficiency and lower cylinder exhaust residuals allow the engine to produce additional torque at lower engine speeds.
The present description may provide several advantages. For example, the approach may improve fuel economy by improving low speed engine torque. Further, the approach may be implemented with a single exhaust manifold and a less complicated fuel control strategy as compared to other approaches. Further still, approach may provide the above advantages at a cost that is lower than other approaches.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.